diagnosing TCC lockup issues.

slowsl

Newbie
Hey guys, I've been dealing with this issue for some months now on the family's DD. Is there a good way to test for a bad torque converter, or if the problem lies in the transmission? The trans currently has about 260,000 miles on it. I rebuilt with new seals and clutch packs, and a new remanufactured torque converter at around 215,000 miles due to a broken sun gear shell. All was good until I was towing home a boat back in January. About 300 miles into the return with the load, the TCC had started locking/unlocking while at steady throttle and highway speeds, as well as a harsh 1-2 shift. It got worse up until the trip ended. We made it back, I researched all the threads and info I could find online. I replaced the shift solenoids, and accumulator, seemed to be the easiest fix. This solved the harsh shift, but after a few days of driving, the TCC lock/unlock issue was back. I think the fresh fluid suppressed the problem for a few days. The next likely suspect was a worn valve body valve.... which I had my doubts considering the symptoms came on out of nowhere. Seems like a worn valve would be a much more gradual problem, but maybe not. Check engine codes are P0B00 (auxiliary transmission fluid pump motor - phase u current malfunction), P1870 (transmission component slipping/transmission mechanical transfer case 4x4 switch circuit failure) Anyway, I installed a Transgo shift kit with the modified tcc valve to solve the worn valve issue, if present. I didn't touch the servo though, which the kit had different springs for, didn't think it had anything to do with the lock/unlock issues. After a few days, everything seemed good, so we took the boat up north, about a 4.5 hour trip. Shortly before our arrival, I could feel the TCC lock/unlock issue was back. It got really bad on our way home, to the point it was slipping so bad, it was always downshifting into 3rd, struggling, and we seemed to have lost 4th gear completely. Once we made it home and the truck sat for a couple days, I went out and drove it, and everything feels normal, shifts into 4th, etc, but the TCC lock/unlock is still present. I'm not towing anything until I know for sure it's fixed. Here is my dilemma. I can get a used trans w/ torque converter for less than $200, but I really don't want to ditch the transmission that I spent a week rebuilding if it's a simple fix which doesn't involve tearing the transmission apart on the bench. I'm starting to suspect a bad torque converter, but I really didn't want to just swap out the torque converter using trial & error, to find out that the problem lies in the transmission, and it needs to all be removed again for a different transmission to be installed. Is there any good way to test the torque converter? Any other suggestions on what to check/replace on the transmission to fix the TCC lock/unlock ussues?
 

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mntegra01

Registered Member
Personal experience here.

I bought a 2003 Shorty TB with 182,000 miles on it with a busted trans pump. I went through it all and replaced almost everything, I even did the sonnax reaming of the valve body and had the new valve installed. I kept getting a P1870 code for TCC issues.

You will keep getting hard shifts because it is sending full line pressure to shift because there is a code present.

I fixed mine by replacing the harness which has the TCC valve built into the trans harness.
 

slowsl

Newbie
Thread Starter
Personal experience here.

I bought a 2003 Shorty TB with 182,000 miles on it with a busted trans pump. I went through it all and replaced almost everything, I even did the sonnax reaming of the valve body and had the new valve installed. I kept getting a P1870 code for TCC issues.

You will keep getting hard shifts because it is sending full line pressure to shift because there is a code present.

I fixed mine by replacing the harness which has the TCC valve built into the trans harness.
Hmmm, I rebuilt the pump about 45k miles ago, when I did all the other stuff. It does still shift fine, no hard shifts, just has the issue of the TCC locking/unlocking all the time at steady throttle above about 45 mph. Is it the TCC solenoid that is hard wired to the wire harness? I had to remove a component from the valve body to get it out that was hard wired into the harness.
 

mntegra01

Registered Member
Not sure. Here's catalog pic of the TCC solenoid. It goes into the pump body. Harness is number 377, and right to lower left of that number is the TCC solenoid. Can kinda see the coil windings and the vertical part goes into the bottom of the pump body.
 

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JerryIrons

Active Member

Not saying that is your problem, but you should probably rule it out. I'm going by memory here and it's known to be faulty, but if it's that brown color it's prone to cracking, I think my article talks about it some.
 

JayArr

Active Member
Why are you towing in drive? Don't you know that's a recipe for failure? Always tow in three. The "hunting" that goes on between 3 and four while in drive causes way to much heat.

Be aware that the TCC normally only locks up in 4th gear EXCEPT if the fluid reaches a high temp (250F? IIRC) then it will attempt to lock up in 2 and 3 as well.

Anyway, I installed a Transgo shift kit with the modified tcc valve to solve the worn valve issue, if present.

In older transmissions, before the PWM system was used, the TCC used to be activated by the Converter Feed Pressure which is a regulated pressure by the Pressure Regulator Valve. Much lower pressure than the Line Pressure. When the engineers decided to add PWM they decided to use the PWM to modulate the Line Pressure directly instead of the Converter Feed Pressure, they probably didn't want to regulate an already regulated pressure, maybe double regulation would cause problems? So the TCC PWM Solenoid Valve modulated fluid that then modulated the line pressure in the Regulator Apply Valve which was then sent to the Torque Converter Clutch.

The Transgo TCC shift kit doesn't "solve" the worn valve issue, it just masks it. What it does is remove the ability of the PCM to modulate the TCC fluid pressure by replacing the Isolator Valve (in the Regulated Apply Valve) with a spring that holds the Regulated Apply Valve wide open.

The result is that the TCC is operated from Line Pressure as high as 140PSI instead of a PWM pressure called "Regulated Apply Pressure" which is between 60 and 80 PSI. It also turns the TCC into an ON or OFF device with nothing in between. This puts a lot of strain on the TCC.

Because the pressure is now so high (Line Level) it masks the fact that the valve is still leaking.

I think the combination of driving in D and having a valve that is still leaking and driving the TC Clutch with line pressure is what is causing your problems.
 

Mooseman

Master Blaster
Moderator
Be aware that the TCC normally only locks up in 4th gear EXCEPT if the fluid reaches a high temp (250F? IIRC) then it will attempt to lock up in 2 and 3 as well.
Hate to disagree but the TCC does engage in 3rd gear. I know because I see it engage with the RPM drop with my tuned PCM which will engage it to 100% without PWM.
 

JayArr

Active Member
Hi Mooseman

I had to go look this up but it appears there is another situation where TCC can be commanded on in 2 or 3.

The transmission must be in hot mode or experiencing a wide open throttle maneuver in order for the TCC to be commanded on in second and third gear. - 4L60E Reference Manual


It's old but scroll down until you see page 63 then read the tan box in the bottom left corner.

The only thing I can think of is that you were in a wide open throttle event or your fluid temp was sufficiently high or your tune changed the PCM programming or the software has been updated since this reference was written.

EDIT: Now that I think about it maybe the fluid temp isn't an error condition so much as a startup condition. I was thinking it only activated in two and three when overheated but it's probably that it won't lock up in 2 and 3 when it's cold.
 
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Mooseman

Master Blaster
Moderator
The fact that mine is tuned is irrelevant. Even the stock tune allows TCC lockup in 3rd while just cruising. Always has. Just slower engagement with PWM.

I don't understand why one would want TCC engagement in WOT because you are demanding max power so to not have the torque multiplication by the converter would be counterintuitive. I'd understand if in an overheat condition that you don't want fluid being sheared in there causing more heat but I doubt that the TCC would be able to hold at WOT. I remember the pre-TCC trannys (i.e. TH350) would get hot from being in continuous slip. Adding TCC had the double benefit of lowering RPMs and heat. The first TCC's were full lockup with no PWM slip but the introduction of PWM reintroduced some heat during the slip portion of TCC engagement.
 

JayArr

Active Member
I found the reference about the temps, it's on page 62 of that series from the reference manual.


Read the italicized paragraph in the bottom right corner.

It says that the TCC is the released position in first, second and third gears but if the fluid goes above 250F the PCM will engage the TCC in second and third gears to reduce the fluid temp.

The ASTM 4L60E codebook says roughly the same thing on page 87

Some trucks, when in “Hot Mode” and TFT is above 250o F (122o C), will allow TCC application in 2nd, 3rd and 4th gears in order to prevent generating heat in the torque converter.

Now I'm confused.
 

Mooseman

Master Blaster
Moderator
That could be the base programming for self preservation but vehicle specific programming may allow TCC lockup in other normal conditions. All the 4L60E trannys I've driven allowed TCC lockup in 3rd.

Just don't let it get hot and you won't have to worry about it :smile:
 

slowsl

Newbie
Thread Starter
Why are you towing in drive? Don't you know that's a recipe for failure? Always tow in three. The "hunting" that goes on between 3 and four while in drive causes way to much heat.

Be aware that the TCC normally only locks up in 4th gear EXCEPT if the fluid reaches a high temp (250F? IIRC) then it will attempt to lock up in 2 and 3 as well.



In older transmissions, before the PWM system was used, the TCC used to be activated by the Converter Feed Pressure which is a regulated pressure by the Pressure Regulator Valve. Much lower pressure than the Line Pressure. When the engineers decided to add PWM they decided to use the PWM to modulate the Line Pressure directly instead of the Converter Feed Pressure, they probably didn't want to regulate an already regulated pressure, maybe double regulation would cause problems? So the TCC PWM Solenoid Valve modulated fluid that then modulated the line pressure in the Regulator Apply Valve which was then sent to the Torque Converter Clutch.

The Transgo TCC shift kit doesn't "solve" the worn valve issue, it just masks it. What it does is remove the ability of the PCM to modulate the TCC fluid pressure by replacing the Isolator Valve (in the Regulated Apply Valve) with a spring that holds the Regulated Apply Valve wide open.

The result is that the TCC is operated from Line Pressure as high as 140PSI instead of a PWM pressure called "Regulated Apply Pressure" which is between 60 and 80 PSI. It also turns the TCC into an ON or OFF device with nothing in between. This puts a lot of strain on the TCC.

Because the pressure is now so high (Line Level) it masks the fact that the valve is still leaking.

I think the combination of driving in D and having a valve that is still leaking and driving the TC Clutch with line pressure is what is causing your problems.
How in the world have I gone 23 years of driving and not known you shouldn't tow in D??? This is the first time I've ever heard this. Just verified in the manual, says to tow in 3rd. I've towed a lot with this truck over the years, boats, cars, supplies, etc. This particular problem started at 260,000+or- miles on the original transmission, so I guess it's held up in D up to this point pretty good, wish I would have known, maybe would have lasted longer, but can't really complain at that mileage. Hmm, strange thing that the Transgo kit didn't seem to do a thing if it was intended to bring pressure up to 140psi, that's a big step up. So the way to properly fix the issue is either to get the kit which reams the hole and provides an oversized valve, or get a new valve body?
Here is where things are at the moment - On someone's suggestion, they mentioned the Fixall valve worked where the Transgo didn't. I installed the Fixall valve and everything seems good. It has o-rings, and also eliminates the PWM. It removes the spring, and has a tail that extends all the way down the bore, so I'm guessing it's supposed to do the same as the Transgo valve, just uses a different method? Right or wrong bandaid, it seems to be driveable, actually shifts better than it ever has with the Transgo kit and the Fixall valve. I towed the boat to a local lake and no slip or hunting TCC, although from now on guess I'll be using 3rd instead of D. The truck itself is old and tired and needs replaced soon. Rust has started and it's beginning to become an eyesore, and a lot of other little issues I can't keep up with anymore. currently test driving a couple other vehicles, but I'd still like to keep it running well until we find another vehicle.
 

Mooseman

Master Blaster
Moderator
It also depends on how heavy the trailer is you're pulling. If it's under 2500#, you could probably get away with towing in OD. However, towing my 2500# covered snowmobile trailer at highway speeds I have to drop it to 3rd because it's like pulling a giant sail. Just check if it's hunting between 3 and 4. Even my Avy with 4.10 gears and 6.0L pulling our 7500# RV trailer I tow in 3rd.
 

JerryIrons

Active Member
You can tow in D, but like mooseman said you have to be careful of the transmission starting that shifting hunting between 3 and 4, it will run hot and shorten the life of your transmission. Towing something through the corn fields of Indiana? D just fine I would think. Pulling a boat through the pennsylvania hills and blind curves? 3 all the way. Where I live it's usually 3 but on occasion I'll go into D.
 

slowsl

Newbie
Thread Starter
Yeah, I know better now. The boat w/ trailer & equipment is probably around 3,900#, and it was towed from the gulf coast up to northern Indiana, the tail end of the trip is when it began the TCC hunting. After the Transgo kit, we went up north 230 miles, and it began acting up near there again.

I should also mention I replaced the lockup solenoid (not the PWM), I looked over it closely and didn't notice any hairline cracks, so I suspect it was still good, but replaced it anyway.
 

Mooseman

Master Blaster
Moderator
At 3900#, definitely tow in 3rd. The TCC may still lock/unlock occasionally on a slight grade or bad headwind but it's way better than hunting between 4 and 3. Also strongly recommend an aux. cooler.
 

slowsl

Newbie
Thread Starter
At 3900#, definitely tow in 3rd. The TCC may still lock/unlock occasionally on a slight grade or bad headwind but it's way better than hunting between 4 and 3. Also strongly recommend an aux. cooler.
I threw it in 3rd gear when there were either a lot of short but frequent or long inclines, whenever the truck felt a bit bogged down. It never once wandered between 3rd & 4th a lot. 99% of the time it was in D though. It would either shift to 3rd while going up an incline, or stay locked solid in 4th on the flat roads. Then again, not something I was paying much attention to, as it never felt like the truck was struggling, ever, until the TCC lock/unlock symptoms popped up back a few months ago, then things got wanky. After quite a few drives, everything seems good now with the Fixall valve, even if it's just a bandaid. I'll report back if it acts up again. Hopefully someone will find this info useful.
 

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